This invention relates generally to cable testing and troubleshooting, and in particular to measuring the attenuation characteristics of cables.
Local Area Networks (LANs) formed by a large number of interconnected computers, work stations, printers, and file servers are becoming increasingly common in the modern office. A LAN system is most commonly implemented by physically connecting all of these devices with copper-conductor, twisted-pair LAN cables, the most common being an eight-wire cable which is configured in four twisted-wire pairs (commonly referred to simply as "twisted pairs") within a flexible wrapper that may include an electrostatic shield, with each end of the cable terminated in an industry-standard connector. A LAN system that has been poorly installed, or has faulty cables or connectors, can result in data transmission errors. Therefore, the LAN system must be tested to verify proper operation and performance.
Attenuation limit is a specified performance parameter required in a LAN certification tool to indicate the maximum signal loss allowable in a given system. Attenuation may be simply a result of the decrease in the power of a signal as it propagates along a cable, or it may be the result of signal loss through a faulty connector. If the attenuation exceeds the specified limit, then the LAN system is not in compliance with performance specifications.
A conventional method of measuring attenuation is to apply a swept-frequency sine wave signal from a remote unit to the opposite end of a twisted pair of wires in the cable and measuring the signal strength at the near end. The sine wave source is incremented in discrete steps across a range of frequencies, while making measurements, and a list of attenuation versus frequency is generated. This list is compared with a worst-case attenuation versus frequency function specified for the cable installation under test to determine compliance--that is, whether or not the attenuation limit is exceeded. However, this conventional method requires a bulky and complex remote unit in addition to the main measurement unit.